Japan: 70 Landing Stations and the World s Most Earthquake-Proof Cable Network

Japan has more submarine cable landing stations than any other country in the world. Seventy sites, scattered across four main islands and dozens of smaller ones, connected by more than fifty cables ranging from an 18-kilometre loop between two villages to transoceanic systems spanning 36,500 km. This is not accident or excess. It is the engineering response of a seismically violent, island-based, export-driven economy that cannot afford a single point of failure in its digital infrastructure.

GeoCables monitors over thirty of these cables through continuous RIPE Atlas measurements. This article presents what our data reveals: which cables carry the fastest traffic, where the bottlenecks are, and why reaching Japan from Europe still takes over 300 milliseconds despite five decades of submarine cable construction.

The Numbers

Japan's submarine cable inventory, by category:

The striking feature is the middle layer: 43 cables under 1,000 km. These are the domestic interconnects — the fibres linking Hokkaido to Honshu, Honshu to Shikoku, Kyushu to Okinawa, and then Okinawa to every inhabited island chain south to Yonaguni, 111 km from Taiwan. No other country has built this many short submarine cables. The reason is geology: Japan is an archipelago sitting on four tectonic plates, and no terrestrial fibre route between its major population centres is safe from earthquake disruption. Submarine cables, buried in the seabed, provide the redundancy that land cables cannot guarantee.

The Two Doors to the World

Japan connects to the global internet through two corridors, and understanding them explains why our measurements from Europe look the way they do.

Door 1: Transpacific (east). Eleven cables cross the Pacific Ocean to the United States — landing at points from Bandon, Oregon to Hermosa Beach, California. These are the fastest paths to North America and, by extension, to the global content networks headquartered there. Our monitoring shows:

The physics floor for a 9,000 km transpacific crossing is approximately 90 ms round-trip. Unity delivers 106 ms — a multiplier of just 1.18×, which is exceptionally tight for a cable of this length. PC-1, a quarter-century old, still achieves 117 ms.

Door 2: South via Southeast Asia (west). The majority of Japan's international cables head south to Singapore, Hong Kong, and the Philippines — the routing hubs of Asia. From there, traffic reaches Europe via the Indian Ocean corridor (SEA-ME-WE, IMEWE, EIG) or connects to Australia, Africa, and the Middle East. Our data for the Japan–Singapore leg:

Japan to Singapore in 75–87 ms is the baseline. Every packet from Europe to Japan that takes the westbound route (Suez → Indian Ocean → Singapore → Japan) adds this segment on top of the Europe–Singapore transit time of approximately 170–200 ms.

The Closest Neighbours

Three cables connect Japan to countries visible from its coastline:

Japan–Korea in 18 ms is one of the fastest international submarine cable connections anywhere. The Korea-Japan Cable Network, operational since 2002, crosses the Korea Strait between Kitakyushu and Busan — a distance shorter than many domestic metropolitan fibre runs. JAKO, entering service in 2027, adds a second parallel crossing via Fukuoka.

The Hokkaido-Sakhalin Cable System (HSCS) is geopolitically remarkable. Built in 2008, it provides a 570 km direct fibre link between Japan and Russia across the La Pérouse Strait. At 21.2 ms average RTT, it is the fastest physical connection between the two countries. The Russia-Japan Cable Network (RJCN), landing at Joetsu and Nakhodka (1,800 km), provides a second, longer path at 46 ms. Both cables continue to carry traffic despite the political tensions that have marked Japan-Russia relations since 2022.

The New Generation

Japan is in the middle of a submarine cable building wave. Six cables with Japanese landing points reached or will reach ready-for-service between 2024 and 2029:

* Apricot's 10.4 ms reading is from a Japan→Indonesia near-end segment, not the full cable length.

The pattern is clear: Meta (Facebook) and Google are the dominant investors in the current wave, with Japanese carriers (NTT, KDDI, SoftBank) as co-investors rather than sole builders. This represents a structural shift from the 1990s–2000s, when cables were built by carrier consortiums. Today's cables are built by content companies who need the capacity for their own traffic — and who sell surplus capacity to everyone else.

Why Europe–Japan Is Still 300 Milliseconds

Our four GeoCables probes — in Jerusalem, Minsk, Tbilisi, and Almaty — measure to Japanese targets (Shima, Maruyama, Nago) at 305–340 ms. This is not because any single link is slow. It is because there is no direct submarine cable between Europe and Japan.

The straight-line distance from Jerusalem to Shima is approximately 9,200 km, giving a physics floor of ~92 ms. The measured 307 ms is a 3.3× multiplier. Where does the overhead come from?

The packet from our European/Middle Eastern probes follows one of two paths:

• Westbound via Suez: Europe → Mediterranean → Suez → Indian Ocean → Singapore (~170–200 ms) → Japan (+75–90 ms) = 250–290 ms plus routing overhead
• Eastbound via USA: Europe → Atlantic → US East Coast (~80 ms) → US West Coast (+60 ms) → Transpacific → Japan (+105 ms) = 250–280 ms plus routing overhead

Both paths traverse approximately 20,000–25,000 km of actual cable. Japan sits at the far end of every intercontinental route from Europe — there is no shortcut. The FLAG Europe-Asia cable (FEA, 1997), which connects the UK to Japan via the Mediterranean, Red Sea, and Indian Ocean, is the closest thing to a direct link, but at 28,000 km it is physically longer than the alternatives and our monitoring shows 285 ms average RTT on it.

Alerts and Stability

In the past 30 days, GeoCables has recorded six anomaly alerts on cables with Japanese landing points:

All six resolved automatically — none escalated beyond a few hours. The most interesting is the "5 Villages 6 Islands" alert: a 2.3× spike on a domestic cable connecting the Izu island chain to the mainland, lasting exactly 59 minutes. This pattern — short, sharp, self-resolving — is typical of planned maintenance windows on Japanese domestic cables, which are among the most rigorously maintained submarine cable systems in the world.

The SJC alert on April 4 was the only one classified as critical (RTT breach above the 4× threshold was triggered by a secondary detection method). At 123 ms against a 107 ms baseline, the actual increase was modest — 15% above normal. It resolved in 4.3 hours.

Six alerts in 30 days across 50+ cables is a low rate. For comparison, COBRAcable (a single 380 km North Sea cable between Denmark and the Netherlands) generated four alerts in the same period. Japan's cable infrastructure, despite its complexity, is remarkably stable.

Earthquakes and Design Philosophy

Japan does not build submarine cables the way most countries do. The archipelago sits at the junction of the Pacific, Philippine Sea, Eurasian, and North American tectonic plates. The 2011 Tōhoku earthquake (magnitude 9.1) severed multiple submarine cables along the Pacific coast, including segments of PC-1 and several domestic systems. Repairs took weeks in some cases.

The engineering response is visible in Japan's cable map: redundancy at every level. Seventy landing stations means that no single station carries irreplaceable traffic. Multiple cables on the transpacific route (Unity, PC-1, FASTER, JUPITER, NCP, TPE) mean that losing one — or even two — leaves the others to absorb the load. The domestic island cables (Izu, Okinawa, Ogasawara chains) are typically built in rings or parallel pairs, never as single-point-of-failure spurs.

NTT, Japan's incumbent carrier, operates the Japan Information Highway (JIH) — a 5,150 km domestic submarine cable network built in 1999 that connects all four main islands plus Okinawa in a continuous ring. This is the backbone that ties everything together: international cables land at coastal stations, and JIH carries the traffic inland. When an earthquake severs one segment, the ring routes traffic the other way.

The Candle Anomaly

One cable in our dataset defies categorisation: Candle, an 8,000 km system scheduled for service in 2028, already shows monitoring data in our system. Its Maruyama→Batam segment averages 6.3 ms — the fastest international submarine cable reading in our entire Japan dataset, and one of the fastest anywhere in our global monitoring. For context, the physics floor for 8,000 km of fibre is approximately 80 ms round-trip. A 6.3 ms reading means we are measuring a near-end segment, not the full cable length — likely the first few hundred kilometres before the signal reaches an intermediate node. But the stability is notable: standard deviation 0.3 ms across 14 samples. Whatever segment we are seeing, it is impeccably clean.

Conclusion

Japan's submarine cable infrastructure is the deepest, most redundant, and most earthquake-hardened in the world. Fifty cables, seventy landing stations, two oceanic corridors, and a domestic ring that ties them together. From our monitoring vantage point, the data tells a story of engineering discipline: six alerts in 30 days, all self-resolving. Transpacific RTTs that have barely changed in 25 years (PC-1's 117 ms in 1999 versus Unity's 106 ms in 2010). And a new generation of hyperscaler-funded cables that is adding capacity faster than traffic can fill it.

The paradox remains: despite all this infrastructure, reaching Japan from Europe still takes 300+ milliseconds. Not because anything is broken, but because the Earth is round and Japan is at the far end of every route from Europe. No cable can fix geometry — but Japan has made sure that every millisecond of that 300 ms journey runs on the best-maintained fibre in the ocean.